The present invention relates to connectors for attaching walls to beams or trusses that are offset from the wall and act as collectors in the lateral force resisting system.
The main purpose of a drag strut connector is to connect a beam or truss to the top plate of a colinear bearing wall, thereby completing the load path and allowing loads to be transferred out of the roof or floor sheathing into the wall system where the shearwalls are. Such a beam or truss is referred to as a load xe2x80x9ccollectorxe2x80x9d or xe2x80x9cdrag strutxe2x80x9d.
In the past, engineers would have to line up the drag strut with the wall, and then use straps and blocking to tie the truss to the wall. The strap accommodated tension loads and the blocking was intended to absorb compression loads (although, in practice, the blocking could not normally be installed tightly enough to work properly). In order to work, the truss had to be lined up directly with the wall, and this required a different setup than the rest of the trusses, which increased the cost of the building.
In order to save this additional cost, the truss can be set back, but this requires a connector that accommodates the offset. In the past, a piece of angle iron, usually 3xe2x80x3xc3x973xe2x80x3, typically of xc2xcxe2x80x3 thickness, was modified by cutting off one leg and it was bolted to the wall top plates and the truss. Bolted connections, however, suffer a number of disadvantages, particularly when resisting shear forces as in the connection of the present invention.
Bolts are larger than screws, so connections must be made with fewer bolts than screws. This means that the percentage of load transferred to each bolt is higher and the pressure exerted by each bolt on the framing members is greater, increasing the chance that the framing members will be damaged by the bolts. Also, if multiple bolts are not all perfectly installed, loading will be uneven and this can cause wood framing members to split. Because screws are smaller than bolts, more can be used to make each connection. Although each individual screw may be weaker than the bolt that would otherwise be used for the connection, the greater number of screws means that the percentage of load transferred to each screw will be less, thereby reducing the chance that the framing members will be damaged by the screws.
Bolts are relatively large, and therefore cannot typically be staggered, and are therefore installed in-line. In a connection like that of the present invention, this means that they act together to damage the framing members, particularly along the grain of wood framing members, which can be split. Because screws are relatively small, screw fastener openings may be staggered, lessening the chance that they will damage and split framing members.
A relatively small number of bolts are used to make a connection, so the spaces between the bolts are relatively large, and these spaces correspond to unreinforced areas of the connector, which may fail by buckling in these areas. Because a relatively large number of screws may be used to make a connection, the spaces between them may be relatively small and the array of screws reinforces the connector against buckling.
Bolts are larger in diameter than screws used for the same application, and the amount of material that must be removed for each fastener from both the connector and the connected members is greater for bolts and creates a weaker connection. Furthermore, it is difficult to accurately cut large bolt holes and this makes it difficult to align large-diameter bolts in a multiple-bolt connection. Because screws are smaller in diameter than bolts, the amount of material that must be removed for each fastener from both the connector and the connected members is less, creating a stronger connection.
Conventionally, the bolt holes in connectors and the bolt holes drilled through wood framing members are {fraction (1/16)}xe2x80x3 larger in diameter than the bolts inserted therethrough. This play in the connection allows for some acceleration of the connector under load, transferring greater stresses to the rest of the building structure and creating impact forces in the bolt holes, thereby increasing the chance that the wood framing members will be split by the bolts. Screw fasteners cannot accelerate under load because there is little or no play in a screw connection, whether the screw is self-drilling and creates its own hole or whether the screw hole is pre-drilled. In neither case is the screw hole oversized. The same is true for the fastener openings that accommodate screws in connectors, which are made to fit the intended screws as closely as possible.
Bolts pass through the members they connect. Under load, torque is generated and the bolts act as wedges, splitting or otherwise damaging the framing members, as in the prior art. Screws do not penetrate through the framing members and therefore do not act as wedges.
The key to the present invention is that it uses self-drilling screws to create a superior connection to that achieved with a similar connector and bolts.
An object of the present invention is to provide a connector that accommodates offset of the connected beams or trusses from the wall.
A further object of the present invention is to provide a connector that can take both compression and tension loads, because the loads being transferred out of the roof or floor truss reverse.
A further object of the present invention is to provide a connector that is more resistant to buckling than the prior art.
A further object of the present invention is to provide a connector that can take higher compression and tension loads than the prior art.
A further object of the present invention is to provide a connector that reduces splitting of the held and holding members as compared to the prior art.
A further object of the present invention is to provide a connector that can be mass-produced.
A further object of the present invention is to provide a connection that is less expensive to make than the prior art.
A further object of the present invention is to provide a connection that is less time-consuming to make than the prior art.